The present invention relates generally to osteosynthesis holding systems, such as those used for stabilization of the spinal column. In particular, a locking mechanism for securing a bone screw to a clamping element of an osteosynthesis holding system is provided. A removal device is provided for removing the bone screw, as a greater axial force is required to overcome the locking mechanism than is needed to engage the locking mechanism. A corresponding method for revision (removal) of the bone screw from the locking mechanism is also provided.
It is well known that in osteosynthesis holding systems in general, and in those systems used for stabilization of the spinal column in particular, a loosening of the bone screw which secures the clamping element to the bone segment occurs. When the bone screw becomes loose, the bone screw may move in an axial direction (i.e. a backing out of the screw may occur). This axial movement may result in a loosening of the entire system, as well as injury to the patient by the protruding screw. For example, injury of blood vessels and nerves in the cervical spine and esophagus are common.
Several alternatives exist for securing the bone screw to the bone plate or clamping element. For example, attachment or locking screws or expansion elements may be used to secure the bone screw in place.
It would be advantageous to provide a locking mechanism for a bone screw where no additional securing elements are necessary. It would be further advantageous to provide a locking mechanism where no active locking of the bone screw is needed. It would be still further advantageous if the connection formed by the locking mechanism is reversible, to provide for explantation (removal) of the bone screw. In addition, it would be advantageous if the locking mechanism allows for a pre-stressing of the bone screw between the clamping element and the bone segment after the locking element is engaged.
The methods and apparatus of the present invention provide the foregoing and other advantages.
The present invention relates to a locking mechanism for securing a bone screw to a clamping element of an osteosynthesis holding system. The bone screw is provided with a circumferential groove located on a top portion of the screw below a screw head. Snap catches are provided on the clamping element. The snap catches protrude from a bone-contacting surface of the clamping element and interlock with the groove in the bone screw when the bone screw is inserted into the clamping element (e.g., when the screw is screwed into a bone segment through a hole in the clamping element). A removal device is provided for removing the bone screw, as a greater axial force is required to overcome the locking mechanism than is needed to engage the locking mechanism. A corresponding method for revision (removal) of the bone screw from the locking mechanism is also provided.
In an exemplary embodiment, a locking mechanism for a bone screw is provided. The locking mechanism includes a clamping element for stabilizing bone segments. The clamping element has at least two snap catches which protrude from a bone-contacting surface of the clamping element and are spaced around an edge of a screw hole. A bone screw is provided which has a circumferential groove located on a top portion thereof below a screw head, for receipt of said snap catches. The snap catches interlock with the groove to secure said bone screw to the clamping element when the bone screw is inserted into the clamping element.
The snap catches may comprise spikes adapted to act as bone anchors. These spikes provide additional anchoring of the clamping element into the bone segment. The spikes may comprise elastic spring elements which snap into the groove when the bone screw is inserted into the clamping element.
In a preferred embodiment, the bone screw is removable from the clamping element after the snap catches interlock with the groove. However, it is preferable if a greater axial force is needed to remove the screw from the clamping element than is needed to insert the screw into the clamping element. Removal of the screw from the clamping element may result in deformation of the snap catches and/or the groove.
The screw may have a shaft having a conical portion between the groove and threads of the shaft. The groove may have a flat edge portion perpendicular to the shaft of the screw. The snap catches may have a square end portion for interlocking with the flat edge portion. Removal of the screw from the clamping element may result in deformation of at least one of (i) the square end portion of the snap catches, or (ii) the flat edge portion of the groove.
A targeting instrument may be placed on the clamping element to provide for correct axial positioning of the screw. The screw is screwed through the clamping element and into the bone segment via the targeting instrument.
The screw may be a cannulated screw. The cannulated screw may be positioned on the bone segment via a Kirschner wire.
The screw may be rotatable after interlocking with the clamping element in order to achieve further pre-stress between the bone segment and the clamping element.
The screw may be a cannulated screw having internal threads in a cannulated portion thereof. The screw may be removable from the clamping element using a removal device having (i) an externally threaded distal end for engagement with the internal threads of the cannulated portion of the screw, and (ii) a handle at a proximal end. The removal device is adapted to be inserted into the screw via a cannulated screwdriver. Removal of the screw is possible by unscrewing the screw from the bone segment using the cannulated screwdriver while simultaneously pulling on the removal device.
The invention further provides for a removal device for revision (removal) of an internally threaded cannulated bone screw. The removal device has a wire body with external threads at a distal end thereof for engagement with the internal threads of the screw. A handle is provided at a proximal end of the wire body for use in pulling the removal device after engagement with the cannulated screw.
The removal device is adapted for insertion into a cannulated instrument, such as a cannulated screwdriver.
The invention also provides a method for revision of an implanted cannulated bone screw. A cannulated screwdriver is inserted into a screw head of the cannulated bone screw. A removal device is inserted into the cannulated screwdriver. An externally threaded distal end of the removal device is screwed into an internally threaded portion of the cannulated screw. Once the removal device is screwed into the cannulated bone screw, the screw can be removed (e.g., from a bone segment) by simultaneously unscrewing the screw using the cannulated screwdriver and pulling the screw using a handle located on a proximal end of the removal device.
The bone screw to be removed may secure a clamping element to a bone segment. A locking mechanism may secure the bone screw to the clamping element. The locking mechanism comprises at least two snap catches protruding from a bone-contacting surface of the clamping element and spaced around an edge of a screw hole. A circumferential groove is located on a top portion of the screw below a screw head for receipt of the snap catches. The snap catches interlock with the groove to secure the bone screw to the clamping element when the bone screw is screwed into the bone segment through the screw hole of the clamping element.
The snap catches may comprise spikes adapted to function as bone anchors. The spikes may comprise elastic spring elements which snap into the groove when the bone screw is inserted into the clamping element. A greater axial force may be needed to remove the screw from the clamping element than is needed to insert the screw into the clamping element. Removal of the screw from the clamping element results in deformation of at least one of (i) the snap catches, or (ii) the groove.
The screw comprises a shaft having a conical portion between the groove and threads of the shaft. The groove may have a flat edge portion perpendicular to a shaft of the screw. The snap catches may have a square end portion for interlocking with the flat edge portion. Removal of the screw from the clamping element results in deformation of at least one of (i) the square end portion of the snap catches, or (ii) the flat edge portion of the groove.
The screw may be rotatable after interlocking with the clamping element in order to achieve further pre-stress between the bone segment and the clamping element.
A method for locking a bone screw to a clamping element is also provided. A clamping element for stabilizing bone segments is provided. The clamping element has at least two snap catches protruding from a bone-contacting surface of the clamping element and spaced around an edge of a screw hole. A bone screw is provided which has a circumferential groove located on a top portion thereof below a screw head, for receipt of said snap catches. The bone screw is screwed into the bone segment through the screw hole of the clamping element until the snap catches interlock with the groove to secure the bone screw to the clamping element.
The snap catches may comprise spikes adapted to function as bone anchors. The spikes may comprise elastic spring elements which snap into the groove when the bone screw is inserted into the clamping element.
The bone screw may be removable from the clamping element after the snap catches interlock with the groove. A greater axial force may be needed to remove the screw from the clamping element than is needed to insert the screw into the clamping element. Removal of the screw from the clamping element may result in deformation of at least one of (i) the snap catches, or (ii) the groove.
The screw may comprise a shaft having a conical portion between the groove and threads of the shaft. The groove may have a flat edge portion perpendicular to a shaft of the screw. The snap catches may have a square end portion for interlocking with the flat edge portion. Removal of the screw from the clamping element may result in deformation of at least one of (i) the square end portion of the snap catches, or (ii) the flat edge portion of the groove.
A targeting instrument may be placed on the clamping element to provide for correct axial positioning of the screw. The screw may be screwed through the clamping element and into the bone segment via the targeting instrument.
The screw may be a cannulated screw. The cannulated screw may be positioned on the bone segment via a Kirschner wire.
The screw may be rotatable after interlocking with the clamping element in order to achieve further pre-stress between the bone segment and the clamping element.
The screw may be a cannulated screw having internal threads in a cannulated portion thereof.